<?php
/**
 * Torrent
 *
 * PHP version 5.2+ (with cURL extention enabled)
 *
 * LICENSE: This source file is subject to version 3 of the GNU GPL
 * that is available through the world-wide-web at the following URI:
 * http://www.gnu.org/licenses/gpl.html. If you did not receive a copy of
 * the GNU GPL License and are unable to obtain it through the web, please
 * send a note to adrien.gibrat@gmail.com so I can mail you a copy.
 *
 * 1) Features:
 * - Decode torrent file or data from local file and distant url
 * - Build torrent from source folder/file(s) or distant url
 * - Super easy usage & syntax
 * - Silent Exception error system
 *
 * 2) Usage example
 * <code>
require_once 'Torrent.php';

// create torrent
$torrent = new Torrent( './path-to-file-or-folder', 'http://torrent.tracker/annonce' );
if ( ! $error = $torrent->error() ) // error method return the last error message
    $torrent->save('test.torrent'); // save to disk
else
    echo '<br>DEBUG: ',$error;

// print torrent infos
$torrent = new Torrent( './test.torrent' );
echo '<pre>private: ', $torrent->is_private() ? 'yes' : 'no',
     '<br>annonce: ';
var_dump( $torrent->announce() );
echo '<br>name: ', $torrent->name(),
     '<br>comment: ', $torrent->comment(),
     '<br>piece_length: ', $torrent->piece_length(),
     '<br>size: ', $torrent->size( 2 ),
     '<br>hash info: ', $torrent->hash_info(),
     '<br>stats: ';
var_dump( $torrent->scrape() );
echo '<br>content: ';
var_dump( $torrent->content() );
echo '<br>source: ',
     $torrent;

// modify torrent
$torrent->announce('http://alternate-torrent.tracker/annonce'); // add a tracker
$torrent->announce(false); // reset announce trackers
$torrent->announce(array('http://torrent.tracker/annonce', 'http://alternate-torrent.tracker/annonce')); // set tracker(s), it also works with a 'one tracker' array...
$torrent->announce(array(array('http://torrent.tracker/annonce', 'http://alternate-torrent.tracker/annonce'), 'http://another-torrent.tracker/annonce')); // set tiered trackers
$torrent->comment('hello world');
$torrent->name('test torrent');
$torrent->is_private(true);
$torrent->httpseeds('http://file-hosting.domain/path/'); // Bittornado implementation
$torrent->url_list(array('http://file-hosting.domain/path/','http://another-file-hosting.domain/path/')); // GetRight implementation

// print errors
if ( $errors = $torrent->errors() ) // errors method return the error stack
    var_dump( '<br>DEBUG: ', $errors );

// send to user
//$torrent->send();
 * </code>
 *
 * @author   Adrien Gibrat <adrien.gibrat@gmail.com>
 * @tester   Jeong, official tester ;) Thanks for your precious feedback
 * @copyleft 2010 - Just use it!
 * @license  http://www.gnu.org/licenses/gpl.html GNU General Public License version 3
 * @version  Release: 1.2 (6 july 2010)
 */
class Torrent {

    /**
    * @const float Default http timeout
    */
    const timeout = 30;

    /**
    * @var array List of error occured
    */
    static protected $errors = array();

    /** Read and decode torrent file/data OR build a torrent from source folder/file(s)
     * Supported signatures:
     * - Torrent(); // get an instance (usefull to scrape and check errors)
     * - Torrent( string $torrent ); // analyse a torrent file
     * - Torrent( string $torrent, string $announce );
     * - Torrent( string $torrent, array $meta );
     * - Torrent( string $file_or_folder ); // create a torrent file
     * - Torrent( string $file_or_folder, string $announce_url, [int $piece_length] );
     * - Torrent( string $file_or_folder, array $meta, [int $piece_length] );
     * - Torrent( array $files_list );
     * - Torrent( array $files_list, string $announce_url, [int $piece_length] );
     * - Torrent( array $files_list, array $meta, [int $piece_length] );
     * @param string|array torrent to read or source folder/file(s) (optional, to get an instance)
     * @param string|array announce url or meta informations (optional)
     * @param int piece length (optional)
     */
    public function __construct ( $data = null, $meta = array(), $piece_length = 256 ) {
        if ( is_null( $data ) )
            return false;
        if ( $piece_length < 32 || $piece_length > 4096 )
            return self::set_error( new Exception( 'Invalid piece lenth, must be between 32 and 4096' ) );
        if ( is_string( $meta ) )
            $meta = array( 'announce' => $meta );
        if ( $this->build( $data, $piece_length * 1024 ) )
            $this->touch();
        else
            $meta = array_merge( $meta, $this->decode( $data ) );
        foreach( $meta as $key => $value )
            $this->{$key} = $value;
    }

    /** Convert the current Torrent instance in torrent format
     * @return string encoded torrent data
     */
    public function __toString() {
        return $this->encode( $this );
    }

    /** Return last error message
     * @return string|boolean last error message or false if none
     */
    public function error() {
        return empty( self::$errors ) ?
            false :
            self::$errors[0]->getMessage();
    }

    /** Return Errors
     * @return array|boolean error list or false if none
     */
    public function errors() {
        return empty( self::$errors ) ?
            false :
            self::$errors;
    }

    /**** Getters and setters ****/

    /** Getter and setter of torrent announce url / list
     * If the argument is a string, announce url is added to announce list (or set as announce if announce is not set)
     * If the argument is an array/object, set announce url (with first url) and list (if array has more than one url), tiered list supported
     * If the argument is false announce url & list are unset
     * @param null|false|string|array announce url / list, reset all if false (optional, if omitted it's a getter)
     * @return string|array|null announce url / list or null if not set
     */
    public function announce ( $announce = null ) {
        if ( is_null( $announce ) )
            return ! isset( $this->{'announce-list'} ) ?
                isset( $this->announce ) ? $this->announce : null :
                $this->{'announce-list'};
        $this->touch();
        if ( is_string( $announce ) && isset( $this->announce ) )
            return $this->{'announce-list'} = self::announce_list( isset( $this->{'announce-list'} ) ? $this->{'announce-list'} : $this->announce, $announce );
        unset( $this->{'announce-list'} );
        if ( is_array( $announce ) || is_object( $announce ) )
            if ( ( $this->announce = self::first_announce( $announce ) ) && count( $announce ) > 1 )
                return $this->{'announce-list'} = self::announce_list( $announce );
            else
                return $this->announce;
        if ( ! isset( $this->announce ) && $announce )
            return $this->announce = (string) $announce;
        unset( $this->announce );
    }

    /** Getter and setter of torrent comment
     * @param null|string comment (optional, if omitted it's a getter)
     * @return string|null comment or null if not set
     */
    public function comment ( $comment = null ) {
        return is_null( $comment ) ?
            isset( $this->comment ) ? $this->comment : null :
            $this->touch( $this->comment = (string) $comment );
    }

    /** Getter and setter of torrent name
     * @param null|string name (optional, if omitted it's a getter)
     * @return string|null name or null if not set
     */
    public function name ( $name = null ) {
        return is_null( $name ) ?
            isset( $this->info['name'] ) ? $this->info['name'] : null :
            $this->touch( $this->info['name'] = (string) $name );
    }

    /** Getter and setter of private flag
     * @param null|boolean is private or not (optional, if omitted it's a getter)
     * @return boolean private flag
     */
    public function is_private ( $private = null ) {
        return is_null( $private ) ?
            ! empty( $this->info['private'] ) :
            $this->touch( $this->info['private'] = $private ? 1 : 0 );
    }

    /** Getter and setter of webseed(s) url list ( GetRight implementation )
     * @param null|string|array webseed or webseeds mirror list (optional, if omitted it's a getter)
     * @return string|array|null webseed(s) or null if not set
     */
    public function url_list ( $urls = null ) {
        return is_null( $urls ) ?
            isset( $this->{'url-list'} ) ? $this->{'url-list'} : null :
            $this->touch( $this->{'url-list'} = is_string( $urls) ? $urls : (array) $urls );
    }

    /** Getter and setter of httpseed(s) url list ( Bittornado implementation )
     * @param null|string|array httpseed or httpseeds mirror list (optional, if omitted it's a getter)
     * @return array|null httpseed(s) or null if not set
     */
    public function httpseeds ( $urls = null ) {
        return is_null( $urls ) ?
            isset( $this->httpseeds ) ? $this->httpseeds : null :
            $this->touch( $this->httpseeds = (array) $urls );
    }

    /**** Analyze BitTorrent ****/

    /** Get piece length
     * @return integer piece length or null if not set
     */
    public function piece_length () {
        return isset( $this->info['piece length'] ) ?
            $this->info['piece length'] :
            null;
    }

    /** Compute hash info
     * @return string hash info or null if info not set
     */
    public function hash_info () {
        return isset( $this->info ) ?
            sha1( self::encode( $this->info ) ) :
            null;
    }

    /** List torrent content
     * @param integer|null size precision (optional, if omitted returns sizes in bytes)
     * @return array file(s) and size(s) list, files as keys and sizes as values
     */
    public function content ( $precision = null ) {
        $files = array();
        if ( isset( $this->info['files'] ) && is_array( $this->info['files'] ) )
            foreach ( $this->info['files'] as $file )
                $files[self::path( $file['path'], $this->info['name'] )] = $precision ?
                    self::format( $file['length'], $precision ) :
                    $file['length'];
        elseif ( isset( $this->info['name'] ) )
                $files[$this->info['name']] = $precision ?
                    self::format( $this->info['length'], $precision ) :
                    $this->info['length'];
        return $files;
    }

    /** List torrent content pieces and offset(s)
     * @return array file(s) and pieces/offset(s) list, file(s) as keys and pieces/offset(s) as values
     */
    public function offset () {
        $files = array();
        $size = 0;
        if ( isset( $this->info['files'] ) && is_array( $this->info['files'] ) )
            foreach ( $this->info['files'] as $file )
                $files[self::path( $file['path'], $this->info['name'] )] = array(
                    'startpiece'    => floor( $size / $this->info['piece length'] ),
                    'offset'    => fmod( $size, $this->info['piece length'] ),
                    'size'      => $size += $file['length'],
                    'endpiece'  => floor( $size / $this->info['piece length'] )
                );
        elseif ( isset( $this->info['name'] ) )
                $files[$this->info['name']] = array(
                    'startpiece'    => 0,
                    'offset'    => 0,
                    'size'      => $this->info['length'],
                    'endpiece'  => floor( $this->info['length'] / $this->info['piece length'] )
                );
        return $files;
    }

    /** Sum torrent content size
     * @param integer|null size precision (optional, if omitted returns size in bytes)
     * @return integer|string file(s) size
     */
    public function size ( $precision = null ) {
        $size = 0;
        if ( isset( $this->info['files'] ) && is_array( $this->info['files'] ) )
            foreach ( $this->info['files'] as $file )
                $size += $file['length'];
        elseif ( isset( $this->info['name'] ) )
                $size = $this->info['length'];
        return is_null( $precision ) ?
            $size :
            self::format( $size, $precision );
    }

    /** Request torrent statistics from scrape page USING CURL!!
     * @param string|array announce or scrape page url (optional, to request an alternative tracker BUT requirered for static call)
     * @param string torrent hash info (optional, requirered ONLY for static call)
     * @param float read timeout in seconds (optional, default to self::timeout 30s)
     * @return array tracker torrent statistics
     */
    /* static */ public function scrape ( $announce = null, $hash_info = null, $timeout = self::timeout ) {
        $packed_hash = urlencode( pack('H*', $hash_info ? $hash_info : $this->hash_info() ) );
        $handles = $scrape = array();
        if ( ! function_exists( 'curl_multi_init' ) )
            return self::set_error( new Exception( 'Install CURL with "curl_multi_init" enabled' ) );
        $curl = curl_multi_init();
        foreach ( (array) ($announce ? $announce : $this->announce()) as $tier )
            foreach ( (array) $tier as $tracker ) {
                $tracker = str_ireplace( array( 'udp://', '/announce', ':80/' ), array( 'http://', '/scrape', '/' ), $tracker );
                if ( isset( $handles[$tracker] ) )
                    continue;
                $handles[$tracker] = curl_init( $tracker . '?info_hash=' . $packed_hash );
                curl_setopt( $handles[$tracker], CURLOPT_RETURNTRANSFER, true );
                curl_setopt( $handles[$tracker], CURLOPT_TIMEOUT, $timeout );
                curl_multi_add_handle( $curl, $handles[$tracker] );
            }
        do {
            while ( ( $state = curl_multi_exec( $curl, $running ) ) == CURLM_CALL_MULTI_PERFORM );
            if( $state != CURLM_OK )
                continue;
            while ( $done = curl_multi_info_read( $curl ) ) {
                $info = curl_getinfo( $done['handle'] );
                $tracker = array_shift( explode( '?', $info['url'], 2 ) );
                if ( empty( $info['http_code'] ) )
                    $scrape[$tracker] = self::set_error( new Exception( 'Tracker request timeout (' . $timeout . 's)' ), true );
                elseif ( $info['http_code'] != 200 )
                    $scrape[$tracker] = self::set_error( new Exception( 'Tracker request failed (' . $info['http_code'] . ' code)' ), true );
                $stats = self::decode_data( curl_multi_getcontent( $done['handle']  ) );
                curl_multi_remove_handle( $curl, $done['handle'] );
                $scrape[$tracker] = empty( $stats['files'] ) ?
                    self::set_error( new Exception( 'Empty scrape data' ), true ) :
                    array_shift( $stats['files'] ) + ( empty( $stats['flags'] ) ? array() : $stats['flags'] );
            }
        } while ( $running );
        curl_multi_close( $curl );
        return $scrape;
    }

    /**** Save and Send ****/

    /** Save torrent file to disk
     * @param null|string name of the file (optional)
     * @return boolean file has been saved or not
     */
    public function save ( $filename = null ) {
        return file_put_contents( is_null( $filename ) ? $this->info['name'] . '.torrent' : $filename, $this->encode( $this ) );
    }

    /** Send torrent file to client
     * @param null|string name of the file (optional)
     * @return void script exit
     */
    public function send ( $filename = null ) {
        $data = $this->encode( $this );
        header( 'Content-type: application/x-bittorrent' );
        header( 'Content-Length: ' . strlen( $data ) );
        header( 'Content-Disposition: attachment; filename="' . ( is_null( $filename ) ? $this->info['name'] . '.torrent' : $filename ) . '"' );
        exit( $data );
    }

    /**** Encode BitTorrent ****/

    /** Encode torrent data
     * @param mixed data to encode
     * @return string torrent encoded data
     */
    static public function encode ( $mixed ) {
        switch ( gettype( $mixed ) ) {
            case 'integer':
            case 'double':
                return self::encode_integer( $mixed );
            case 'object':
                $mixed = (array) $mixed; //Thanks to W-Shadow: http://w-shadow.com/blog/2008/11/11/parse-edit-and-create-torrent-files-with-php/
            case 'array':
                return self::encode_array( $mixed );
            default:
                return self::encode_string( (string) $mixed );
        }
    }

    /** Encode torrent string
     * @param string string to encode
     * @return string encoded string
     */
    static private function encode_string ( $string ) {
        return strlen( $string ) . ':' . $string;
    }

    /** Encode torrent integer
     * @param integer integer to encode
     * @return string encoded integer
     */
    static private function encode_integer ( $integer ) {
        return 'i' . $integer . 'e';
    }

    /** Encode torrent dictionary or list
     * @param array array to encode
     * @return string encoded dictionary or list
     */
    static private function encode_array ( $array ) {
        if ( self::is_list( $array ) ) {
            $return = 'l';
            foreach ( $array as $value )
                $return .= self::encode( $value );
        } else {
            ksort( $array, SORT_STRING );
            $return = 'd';
            foreach ( $array as $key => $value )
                $return .= self::encode( strval( $key ) ) . self::encode( $value );
        }
        return $return . 'e';
    }

    /**** Decode BitTorrent ****/

    /** Decode torrent data or file
     * @param string data or file path to decode
     * @return array decoded torrent data
     */
    static protected function decode ( $string ) {
        $data = is_file( $string ) || self::url_exists( $string ) ?
            self::file_get_contents( $string ) :
            $string;
        return (array) self::decode_data( $data );
    }

    /** Decode torrent data
     * @param string data to decode
     * @return array decoded torrent data
     */
    static private function decode_data ( & $data ) {
        switch( self::char( $data ) ) {
        case 'i':
            $data = substr( $data, 1 );
            return self::decode_integer( $data );
        case 'l':
            $data = substr( $data, 1 );
            return self::decode_list( $data );
        case 'd':
            $data = substr( $data, 1 );
            return self::decode_dictionary( $data );
        default:
            return self::decode_string( $data );
        }
    }

    /** Decode torrent dictionary
     * @param string data to decode
     * @return array decoded dictionary
     */
    static private function decode_dictionary ( & $data ) {
        $dictionary = array();
        $previous = null;
        while ( ( $char = self::char( $data ) ) != 'e' ) {
            if ( $char === false )
                return self::set_error( new Exception( 'Unterminated dictionary' ) );
            if ( ! ctype_digit( $char ) )
                return self::set_error( new Exception( 'Invalid dictionary key' ) );
            $key = self::decode_string( $data );
            if ( isset( $dictionary[$key] ) )
                return self::set_error( new Exception( 'Duplicate dictionary key' ) );
            if ( $key < $previous )
                return self::set_error( new Exception( 'Missorted dictionary key' ) );
            $dictionary[$key] = self::decode_data( $data );
            $previous = $key;
        }
        $data = substr( $data, 1 );
        return $dictionary;
    }

    /** Decode torrent list
     * @param string data to decode
     * @return array decoded list
     */
    static private function decode_list ( & $data ) {
        $list = array();
        while ( ( $char = self::char( $data ) ) != 'e' ) {
            if ( $char === false )
                return self::set_error( new Exception( 'Unterminated list' ) );
            $list[] = self::decode_data( $data );
        }
        $data = substr( $data, 1 );
        return $list;
    }

    /** Decode torrent string
     * @param string data to decode
     * @return string decoded string
     */
    static private function decode_string ( & $data ) {
        if ( self::char( $data ) === '0' && substr( $data, 1, 1 ) != ':' )
            self::set_error( new Exception( 'Invalid string length, leading zero' ) );
        if ( ! $colon = @strpos( $data, ':' ) )
            return self::set_error( new Exception( 'Invalid string length, colon not found' ) );
        $length = intval( substr( $data, 0, $colon ) );
        if ( $length + $colon + 1 > strlen( $data ) )
            return self::set_error( new Exception( 'Invalid string, input too short for string length' ) );
        $string = substr( $data, $colon + 1, $length );
        $data = substr( $data, $colon + $length + 1 );
        return $string;
    }

    /** Decode torrent integer
     * @param string data to decode
     * @return integer decoded integer
     */
    static private function decode_integer ( & $data ) {
        $start = 0;
        $end    = strpos( $data, 'e');
        if ( $end === 0 )
            self::set_error( new Exception( 'Empty integer' ) );
        if ( self::char( $data ) == '-' )
            $start++;
        if ( substr( $data, $start, 1 ) == '0' && ( $start != 0 || $end > $start + 1 ) )
            self::set_error( new Exception( 'Leading zero in integer' ) );
        if ( ! ctype_digit( substr( $data, $start, $end ) ) )
            self::set_error( new Exception( 'Non-digit characters in integer' ) );
        $integer = substr( $data, 0, $end );
        $data = substr( $data, $end + 1 );
        return $integer + 0;
    }

    /**** Internal Helpers ****/

    /** Build torrent info
     * @param string|array source folder/file(s) path
     * @param integer piece length
     * @return array|boolean torrent info or false if data isn't folder/file(s)
     */
    protected function build ( $data, $piece_length ) {
        if ( is_null( $data ) )
            return false;
        elseif ( is_array( $data ) && self::is_list( $data ) )
            return $this->info = $this->files( $data, $piece_length );
        elseif ( is_dir( $data ) )
            return $this->info = $this->folder( $data, $piece_length );
        elseif ( ( is_file( $data ) || self::url_exists( $data ) ) && ! self::is_torrent( $data ) )
            return $this->info = $this->file( $data, $piece_length );
        else
            return false;
    }

    /** Set torrent creator and creation date
     * @param any param
     * @return any param
     */
    protected function touch ( $void = null ) {
        $this->{'created by'}       = 'Torrent PHP Class - Adrien Gibrat';
        $this->{'creation date'}    = time();
        return $void;
    }

    /** Add an error to errors stack
     * @param Exception error to add
     * @param boolean return error message or not (optional, default to false)
     * @return boolean|string return false or error message if requested
     */
    static protected function set_error ( $exception, $message = false ) {
        return ( array_unshift( self::$errors,  $exception ) && $message ) ? $exception->getMessage() : false;
    }

    /** Build announce list
     * @param string|array announce url / list
     * @param string|array announce url / list to add (optionnal)
     * @return array announce list (array of arrays)
     */
    static protected function announce_list( $announce, $merge = array() ) {
        return array_map( create_function( '$a', 'return (array) $a;' ), array_merge( (array) $announce, (array) $merge ) );
    }

    /** Get the first announce url in a list
     * @param array announce list (array of arrays if tiered trackers)
     * @return string first announce url
     */
    static protected function first_announce( $announce ) {
        while ( is_array( $announce ) )
            $announce = reset( $announce );
        return $announce;
    }

    /** Helper to pack data hash
     * @param string data
     * @return string packed data hash
     */
    static protected function pack ( & $data ) {
        return pack('H*', sha1( $data ) ) . ( $data = null );
    }

    /** Helper to build file path
     * @param array file path
     * @param string base folder
     * @return string real file path
     */
    static protected function path ( $path, $folder ) {
        array_unshift( $path, $folder );
        return join( DIRECTORY_SEPARATOR, $path );
    }

    /** Helper to test if an array is a list
     * @param array array to test
     * @return boolean is the array a list or not
     */
    static protected function is_list ( $array ) {
        foreach ( array_keys( $array ) as $key )
            if ( ! is_int( $key ) )
                return false;
        return true;
    }

    /** Build pieces depending on piece length from a file handler
     * @param ressource file handle
     * @param integer piece length
     * @param boolean is last piece
     * @return string pieces
     */
    private function pieces ( $handle, $piece_length, $last = true ) {
        static $piece, $length;
        if ( empty( $length ) )
            $length = $piece_length;
        $pieces = null;
        while ( ! feof( $handle ) ) {
            if ( ( $length = strlen( $piece .= fread( $handle, $length ) ) ) == $piece_length )
                $pieces .= self::pack( $piece );
            elseif ( ( $length = $piece_length - $length ) < 0 )
                return self::set_error( new Exception( 'Invalid piece length!' ) );
        }
        fclose( $handle );
        return $pieces . ( $last && $piece ? self::pack( $piece ) : null);
    }

    /** Build torrent info from single file
     * @param string file path
     * @param integer piece length
     * @return array torrent info
     */
    private function file ( $file, $piece_length ) {
        if ( ! $handle = self::fopen( $file, $size = self::filesize( $file ) ) )
            return self::set_error( new Exception( 'Failed to open file: "' . $file . '"' ) );
        return array(
            'length'    => $size,
            'name'      => end( explode( DIRECTORY_SEPARATOR, $file ) ),
            'piece length'  => $piece_length,
            'pieces'    => $this->pieces( $handle, $piece_length )
        );
    }

    /** Build torrent info from files
     * @param array file list
     * @param integer piece length
     * @return array torrent info
     */
    private function files ( $files, $piece_length ) {
        $files = array_map( 'realpath', $files );
        sort( $files );
        usort( $files, create_function( '$a,$b', 'return strrpos($a,DIRECTORY_SEPARATOR)-strrpos($b,DIRECTORY_SEPARATOR);' ) );
        $path   = explode( DIRECTORY_SEPARATOR, dirname( realpath( current( $files ) ) ) );
        $pieces = null; $info_files = array(); $count = count($files) - 1;
        foreach ( $files as $i => $file ) {
            if ( $path != array_intersect_assoc( $file_path = explode( DIRECTORY_SEPARATOR, $file ), $path ) )
                self::set_error( new Exception( 'Files must be in the same folder: "' . $file . '" discarded' ) );
            if ( ! $handle = self::fopen( $file, $filesize = self::filesize( $file ) ) )
                self::set_error( new Exception( 'Failed to open file: "' . $file . '" discarded' ) );
            $pieces .= $this->pieces( $handle, $piece_length, $count == $i );
            $info_files[] = array(
                'length'    => $filesize,
                'path'      => array_diff( $file_path, $path )
            );
        }
        return array(
            'files'     => $info_files,
            'name'      => end( $path ),
            'piece length'  => $piece_length,
            'pieces'    => $pieces
        );

    }

    /** Build torrent info from folder content
     * @param string folder path
     * @param integer piece length
     * @return array torrent info
     */
    private function folder ( $dir, $piece_length ) {
        return $this->files( self::scandir( $dir ), $piece_length );
    }

    /** Helper to return the first char of encoded data
     * @param string encoded data
     * @return string|boolean first char of encoded data or false if empty data
     */
    static private function char ( $data ) {
        return empty( $data ) ?
            false :
            substr( $data, 0, 1 );
    }

    /**** Public Helpers ****/

    /** Helper to format size in bytes to human readable
     * @param integer size in bytes
     * @param integer precision after coma
     * @return string formated size in appropriate unit
     */
    static public function format ( $size, $precision = 2 ) {
        $units = array ('octets', 'Ko', 'Mo', 'Go', 'To');
        while( ( $next = next( $units ) ) && $size > 1024 )
            $size /= 1024;
        return round( $size, $precision ) . ' ' . ( $next ? prev( $units ) : end( $units ) );
    }

    /** Helper to return filesize (even bigger than 2Gb -linux only- and distant files size)
     * @param string file path
     * @return double|boolean filesize or false if error
     */
    static public function filesize ( $file ) {
        if ( is_file( $file ) )
            return (double) sprintf( '%u', @filesize( $file ) );
        else if ( $content_length = preg_grep( $pattern = '#^Content-Length:\s+(\d+)$#i', (array) @get_headers( $file ) ) )
            return (int) preg_replace( $pattern, '$1', reset( $content_length ) );
    }

    /** Helper to open file to read (even bigger than 2Gb, linux only)
     * @param string file path
     * @param integer|double file size (optional)
     * @return ressource|boolean file handle or false if error
     */
    static public function fopen ( $file, $size = null ) {
        if ( ( is_null( $size ) ? self::filesize( $file ) : $size ) <= 2 * pow( 1024, 3 ) )
            return fopen( $file, 'r' );
        elseif ( PHP_OS != 'Linux' )
            return self::set_error( new Exception( 'File size is greater than 2GB. This is only supported under Linux' ) );
        elseif ( ! is_readable( $file ) )
            return false;
        else
            return popen( 'cat ' . escapeshellarg( realpath( $file ) ), 'r' );
    }

    /** Helper to scan directories files and sub directories recursivly
     * @param string directory path
     * @return array directory content list
     */
    static public function scandir ( $dir ) {
        $paths = array();
        foreach ( scandir( $dir ) as $item )
                if ( $item != '.' && $item != '..' )
                    if ( is_dir( $path = realpath( $dir . DIRECTORY_SEPARATOR . $item ) ) )
                        $paths = array_merge( self::scandir( $path ), $paths );
                    else
                        $paths[] = $path;
        return $paths;
    }

    /** Helper to check if url exists
     * @param string url to check
     * @return boolean does the url exist or not
     */
    static public function url_exists ( $url ) {
        return preg_match( '#^http(s)?://[a-z0-9-]+(.[a-z0-9-]+)*(:[0-9]+)?(/.*)?$#i', $url ) ?
            (bool) preg_grep( '#^HTTP/.*\s(200|304)\s#', (array) @get_headers( $url ) ) :
            false;
    }

    /** Helper to check if a file is a torrent
     * @param string file location
     * @param float http timeout (optional, default to self::timeout 30s)
     * @return boolean is the file a torrent or not
     */
    static public function is_torrent ( $file, $timeout = self::timeout ) {
        return self::file_get_contents( $file, $timeout, 0, 11 ) === 'd8:announce';
    }

    /** Helper to get (distant) file content
     * @param string file location
     * @param float http timeout (optional, default to self::timeout 30s)
     * @param integer starting offset (optional, default to null)
     * @param integer content length (optional, default to null)
     * @return string|boolean file content or false if error
     */
    static public function file_get_contents ( $file, $timeout = self::timeout, $offset = null, $length = null ) {
        if ( is_file( $file ) || ini_get( 'allow_url_fopen' ) ) {
            $context = ! is_file( $file ) && $timeout ? 
                stream_context_create( array( 'http' => array( 'timeout' => $timeout ) ) ) : 
                null;
            return ! is_null( $offset ) ? $length ?
                @file_get_contents( $file, false, $context, $offset, $length ) : 
                @file_get_contents( $file, false, $context, $offset ) : 
                @file_get_contents( $file, false, $context );
        } elseif ( ! function_exists( 'curl_init' ) )
            return self::set_error( new Exception( 'Install CURL or enable "allow_url_fopen"' ) );
        $handle = curl_init( $file );
        if ( $timeout )
            curl_setopt( $handle, CURLOPT_TIMEOUT, $timeout );
        if ( $offset || $length )
            curl_setopt( $handle, CURLOPT_RANGE, $offset . '-' . ( $length ? $offset + $length -1 : null ) );
        curl_setopt( $handle, CURLOPT_RETURNTRANSFER, 1 );
        $content = curl_exec( $handle );
        $size = curl_getinfo( $handle, CURLINFO_CONTENT_LENGTH_DOWNLOAD );
        curl_close( $handle );
        return ( $offset && $size == -1 ) || ( $length && $length != $size ) ? $length ?
            substr( $content, $offset, $length) :
            substr( $content, $offset) :
            $content;
    }

}